In liquid chromatography it has been a problem to provide means to inject discrete liquid samples into a liquid chromatograph column with a minimum of dilution of "peak-spreading" as it is called in the chromatographic art. Applicant set out to provide an apparatus useful in the injection to an l.c. column sequence of a large number of liquid samples. Such sequential testing apparatus is known to be useful in such testing procedures as quality control testing in the pharmaceutical industry and the like.
In general, the schematic injection scheme selected by the Applicant is that disclosed in U.S. Pat. No. 3,916,692 to Abrahams. Applicant, in adapting that scheme to a reciprocating sampling conduit adapted to enter a series of sample containers encountered a number of design problems, the most critical of which was the sealing of the outlet of the reciprocating sample conduit into the liquid chromatographic flow circuit. It is to be understood that in the chromatographic processes being discussed, fluids are handled at pressures of 5000 psig and even higher.
As will be described below, the particular apparatus constructed to meet the various problems meets, and even surpasses, the prior standard of performance established by the apparatus described in U.S. Pat. No. 3,916,692.
In liquid chromatography and numerous other analytical procedures in the chemical and medical arts, it is desirable to have a large number of samples handled sequentially on the same apparatus. In such cases, a conduit, often a hypodermic needle or the like, is dipped into a series of different samples. In such situations, there is an increased danger of cross-sample contamination because of sample from an earlier operation being dipped into a second operation.
It has been a problem in the art to provide a drip-proof, conduit-cleaning procedure which can be rapidly used without slowing the sample feeding procedure. As will be described below, Applicant has, for the first time, achieved such a drip proof, contamination avoiding, conduit cleaning means. This apparatus is particularly valuable in conjunction with automatic liquid sampling apparatus in liquid chromatography.